The present invention relates generally to mixing and dispensing nozzles, and more particularly, to a so-called anti-crossover or crossover-resistant nozzle for use with multi-component systems, particularly urethane foams. In particular, the invention relates to readily attachable, disposable nozzles having two principal pieces that snap together, and two more additional pieces or components making up the entire nozzle. According to the invention, the nozzles can be reusable with a non-reacting foam or may be used again by flushing with solvent. Such nozzles, according to the invention, have both an anti-crossover feature and a snap-together assembly and are associated in use with a dispenser such as a foam gun for dispensing foam, or other device for dispensing a bead, spray or fillet of a foam insulation or like material.
In the prior art, a number of nozzles have been available for use with such dispensers, (most of which are commonly referred to as guns). However, most if not all of such nozzles did not have an inherent feature which prevents so-called crossover in use. Neither were they a molded, snap-together type construction. In a two-component urethane gun, both the isocyanate component and the resin component are metered under a supply pressure to a disposable mixing nozzle. Such a device, for example, was made by the assignee of the Brooks U.S. Pat. No. 3,784,110, which was the first commercially successful two-component foam gun having a disposable or throwaway nozzle.
A disposable low cost nozzle is important for multi-component mixing and metering systems, because, after a short time, (from one-half a minute to two minutes), the components making up the mix or other thermosets react to cure and set up in the nozzle, and thereby render further mixing, particularly on ratio mixing of reactants difficult or impossible. Once used in a properly functioning gun, the mixing nozzle is simply removed and thrown away. This technique avoids the use of costly, and potentially harmful solvents for flushing.
In one use, the isocyanate component and the resin component are simultaneously admitted to a mixing nozzle in a predetermined ratio. This ratio is determined by the design of the system, chemistry of the reactants, and particularly by the size of the orifices leading into the nozzle passages, and by the supply pressure under which the components are maintained.
In one method, which uses aerosol type reactants, when the dispenser trigger is actuated, two valves open simultaneously and a desired proportion of each component is injected by the material supply force through the nozzle orifices and into the mixing and dispensing nozzle. Upon entering the mixing and dispensing nozzle, both the materials instantaneously experience a pressure drop, causing the gas in the material to expand rapidly as it passes along the mixing elements of the mixing nozzle. This expansion of materials creates turbulence and continues to mix as the reactants travel forward along the mix path of the nozzle. This mixing initiates a chemical reaction between the components, which causes the reactants to polymerize.
As the polymerizing mass exits the nozzle, it is under great force due to the supply pressure, vaporization of the blowing agents, along with the energy and gas generation created through the polymerizing reaction. Upon leaving the nozzle, the discharge pattern of the reacting material can be defined and controlled by any of a number of nozzle geometries resulting in a high force spray pattern, or a much lower force pour pattern, depending on the application.
In another practice of the art as described in U.S. Pat. No. 5,529,245, non-aerosol type of reactants are processed through a mixing nozzle as described in this invention. In this method, non-aerosol materials are delivered via the supply pressure through the dispenser--once activated--into a mixing nozzle of the current invention. The two materials are injected by the material supply force through the nozzle orifices and into the mixing nozzle. Upon entering the mixing nozzle, the materials are mixed by turbulent flow as the material travels through the mixer.
The mixing initiates a chemical reaction within the nozzle and in the case of some foaming materials, CO.sub.2 is generated in the reaction, causing the polymerizing mass to expand. In this method, if a spray pattern is desired, a third stream of gas is delivered through the nozzle to the tip where the material exits. This gas stream is used to assist in spraying the mixed polymerizing material onto the substrate. As in the previously described embodiment, the reacting material can be defined by any of a number of nozzle geometries.
Past experience has proven that there are some shortcomings to the old mixing nozzle design. In previous mixing nozzle designs there are circumstances that can occur during the course of mixing that create an opportunity for one or more of the reactants to flow rearward into the passages of the dispenser.
This rearward flow creates or allows a condition of chemical reaction within the dispenser, causing the passages of the dispenser to be clogged with reacted material. This situation, commonly referred to as "crossover", is the major cause of product failure with these types of dispensing systems. When the passages of the dispenser system become clogged, the system is now rendered either completely useless, or at least useless to meter components "on ratio", due to the complete or partial blockages in one passage or another.
There are several common conditions that create the opportunity for crossover. One of the most common conditions occurs where the operator, upon first starting the operation of the kit, fails to open both supply lines to the dispenser. Thus, when the dispenser is activated, only one component enters the mixing chamber. At this time, there is no competing pressure or flow from the other supply port of the valve or mixer inlet, and consequently, nothing to prevent the single component within the mixer from flowing rearwardly out the other inlet passage and into the dispenser.
Once the operator realizes that only one component is flowing, he understands the problem. Then he opens the second supply valve and pressurizes the dispenser with the second, previously missing component. At that time the second component mixes with the first in the dispenser valve and hoses with the "crossed over" component, thus causing a reaction and fouling the dispenser.
A second situation occurs when the operator activates the dispenser with a previously used and clogged or partially clogged nozzle. At this time, and according to the pressure within the system at this time, the nozzle is charged with more reactants but the outlet passage of the nozzle is blocked. This produces a situation wherein the reactants are reacting and generating high pressures internally within the mixing nozzle.
Because the discharge tip is blocked reactants cannot be discharged from the end of the nozzle, the reacting, and hence expanding material continues to expand forcibly within the nozzle. If, at this time, the operator pulls the trigger of the dispenser without ejecting the nozzle, a crossover condition arises due to the rearward flow by the reacting material into the dispenser. This rearward drive is created due to the higher pressure present in the nozzle when compared to the line pressure feeding the dispenser. Particularly when portable kits are used that are not full and/or at the highest pressure, the pressure created in this type of crossover within the nozzle can overcome the supply pressure and drive reacting material rearward into the dispenser, thus fouling the dispenser.
A third crossover condition exists as a result of simple pressure differences occurring between the two pressure streams, where one stream is strong enough to overcome the other, forcing a condition of rearward flow of the component that otherwise would be urged into the nozzle under the lower or weaker pressure. This particularly occurs if a new container is used with an old or nearly-exhausted one. This situation also arises when using supply pumps and there is a pump failure.
Accordingly, it is an object of the present invention to provide an improved mixing and dispensing nozzle for urethane foam or similar multi-component systems.
Another object of the invention is to provide mixing and dispensing nozzle components which can be assembled by the simple process of snapping one component inside the other, thereby trapping the third component in the dispenser, with the anti-crossover valves being secured in place.
Yet another object of the invention is to provide a mixing and dispensing nozzle which contains an internal set of valve leaflets normally serving to close off the rearward flow of material into the dispenser or gun.
Still another object of the invention is to provide a combination of a multi-piece nozzle which can be easily assembled, together with leaflet style valves restricting crossover contamination in the use of the apparatus.
A further object of the invention is to provide a multi-piece nozzle which includes a baffle mixing element having vanes disposed around a central backbone and having the backbone engage the rear wall of one of the components of the valve as an aid to assembly.
A still further object of the invention is to provide a valve for each of plural inlets and having a single leaflet, made from a thin sheet of plastic film such as a polypropylene, a polyester or the like.
An additional object of the invention is to provide a single valve assembly comprising a pair of leaflets disposed to either side of a thermally welded or mechanically or adhesively affixed portion which attaches the center portion of the leaflet to the rear wall of the nozzle.
Another object of the invention is to provide a nozzle that snaps together and includes wings or finger-gripping handles on the body of the nozzle. A still further object is to provide a snap-together construction which includes a molded-in rib or gasket between the sections to insure a tight fit.
The invention achieves its objects and advantages in two ways. The first is to provide a telescoping, snap action type assembly for mixing and dispensing nozzles, with optional wings or finger-gripping portions, and the other is to provide a valve, preferably in the form of leaflets, for two or more inlet openings, with the valve leaflets extending over the opening and closing them off by their own innate resiliency, and remain forcibly closed by the internal pressure within the mixing nozzle. At the same time, ready opening occurs under the force of incoming liquid components, with the valve leaflets being preferably affixed to the rear wall of the nozzle by thermal attachment, by an adhesive, or mechanical entrapment.
The manner in which these objects and advantages are achieved in practice will become more clearly apparent when taken in connection with a detailed description of the preferred embodiments of the invention set forth by way of example and shown in the accompanying drawings, in which like reference numbers indicate the corresponding parts throughout.